This invention relates to coated abrasive articles and more particularly, to such articles which incorporate energy curable compositions containing an epoxy resin and an ethylene vinyl acetate copolymer or an epoxy resin, an ethylene vinyl acetate copolymer and an acrylate.
Coated abrasives generally comprise a flexible backing upon which a binder supports a coating of abrasive particles. The abrasive particles are typically secured to the backing by a first binder, commonly referred to as a make coat. Additionally, the abrasive particles are generally oriented with their longest dimension perpendicular to the backing to provide an optimum cut rate. A second binder, commonly referred to as a size coat, is then applied over the make coat and the abrasive particles to anchor the particles to the backing.
Porous cloth, fabric and textile materials are frequently used as backings for coated abrasive articles. The make coat precursor is typically applied to the backing as a low viscosity material. In this condition, the make coat precursor can infiltrate into the interstices of the porous backing leaving an insufficient coating thickness making it difficult to bond the subsequently applied abrasive particles to the backing and, on curing, resulting in the backing becoming stiff, hard and brittle. As a result, it has become conventional to employ one or more treatment coats, such as a presize, saturant coat, backsize or a subsize coat, to seal the porous backing.
The presize, saturant coat, backsize and subsize coat typically involve thermally curable resinous adhesives, such as phenolic resins, epoxy resins, acrylate resins, acrylic latices, urethane resins, glue, starch and combinations thereof. A saturant coat saturates the cloth and fills pores, resulting in a less porous, stiffer cloth with more body. An increase in body provides an increase in strength and durability of the article. A presize coat, which is applied to the front side of the backing, may add bulk to the cloth and may improve adhesion of subsequent coatings. A backsize coat, which is applied to the back side of the backing, that is, the side opposite that to which the abrasive grains are applied, adds body to the backing and protects the yarns of the cloth from wear. A subsize coat is similar to a saturation coat except that it is applied to a previously treated backing. The drawback of such a presize, saturant coat, backsize and subsize coat is that it entails added processing step(s) which increase the cost and complexity of manufacturing. Similarly, paper backings may be treated to prevent penetration of make adhesives and/or to waterproof.
This invention generally relates to a coated abrasive article utilizing an improved make coat formulation. The coated abrasive article includes a backing, the improved make coat on the backing, and a plurality of abrasive particles at least partially embedded in the make coat. The make coat also may be referred to herein as the first binder.
The present invention provides a coated abrasive article, comprising:
a) a backing having a front surface and a back surface;
b) a crosslinked first binder on said front surface of said backing, wherein said first binder is formed from a first binder precursor, said first binder precursor is an energy-curable composition made by mixing the following components
i) about 2 to about 99 weight percent of an epoxy resin, the weight percent being based on the total resin content;
ii) about 1 to about 98 weight percent of an ethylene-vinyl acetate copolymer resin, the weight percent being based on the total resin content;
iii) an effective amount of a curing agent for crosslinking said epoxy resin; and
c) a plurality of abrasive particles, wherein said abrasive particles are at least partially embedded in said first binder.
The above binder precursor compositions of the invention are homogeneous in the molten state and are preferably free from, that is, do not contain, hydrocarbon polyolefin resins. xe2x80x9cHydrocarbon polyolefin resinxe2x80x9d refers to a fully prepolymerized uncrosslinked polymeric hydrocarbon bearing essentially no organic functional groups, prepared from homopolymerization and/or copolymerization of an olefinic monomer(s). Such resins can be incompatible with epoxy resins and can cause phase separation of compositions containing an appreciable amount of epoxy resin. Examples of such resins include polyethylene, polypropylene, and the like, and poly(ethylene-co-propylene), poly(propylene-co-1-butene), and the like.
In another aspect, the present invention provides a coated abrasive article, comprising:
a) a backing having a front surface and a back surface;
b) a crosslinked first binder on said front surface of said backing, wherein said first binder is formed from a first binder precursor, said first binder precursor is an energy-curable composition made by mixing the following components
i) about 2 to about 98 weight percent of an epoxy resin, the weight percent being based on the total resin content;
ii) about 1 to about 90 weight percent of an ethylene-vinyl acetate copolymer resin, the weight percent being based on the total resin content;
iii) about 0.1 to about 20 weight percent of a polyfunctional acrylate, the weight percent being based on the total resin content;
iv) an effective amount of a curing agent for crosslinking said epoxy resin; and
c) a plurality of abrasive particles, wherein said abrasive particles are at least partially embedded in said first binder.
In another aspect, the present invention provides an energy-curable composition made by mixing components comprising:
a) an epoxy resin;
b) an ethylene-vinyl acetate copolymer resin;
c) a polyfunctional acrylate; and
d) an effective amount of a curing agent for crosslinking said epoxy resin.
In another aspect, the present invention provides a presized backing for a coated abrasive article comprising:
a) a backing suitable for use in a coated abrasive article; and
b) a crosslinked presize layer on the backing formed from a presize binder precursor, wherein the presize binder precursor is an energy curable composition comprising:
i) from about 30 to about 95 weight percent of an epoxy resin, the weight percent being based on the total resin content,
ii) from about 5 to about 70 weight percent an ethylene-vinyl acetate copolymer resin, the weight percent being based on the total resin content, and
iii) an effective amount of a curing agent for crosslinking said epoxy resin.
In another aspect, the present invention provides a presized backing for a coated abrasive article comprising:
a) a backing suitable for use in a coated abrasive article; and
b) a crosslinked presize layer on the backing formed from a presize binder precursor, wherein the presize binder precursor is an energy curable composition comprising:
i) about 2 to about 98 weight percent of an epoxy resin, the weight percent being based on the total resin content,
ii) about 1 to about 90 weight percent of an ethylene-vinyl acetate copolymer resin, the weight percent being based on the total resin content,
iii) about 0.1 to about 20 weight percent of a polyfunctional acrylate component, the weight percent being based on the total resin content, and
iv) an effective amount of a curing agent for crosslinking said epoxy resin.
The above binder precursors of the invention are preferably melt processable.
As used herein, a xe2x80x9chot meltxe2x80x9d refers to a composition that is a solid at room temperature (about 20 to 22xc2x0 C.) but which, upon heating, melts to a viscous liquid that can be readily applied to a coated abrasive article backing. A xe2x80x9cmelt processablexe2x80x9d composition refers to a composition that can transform, for example, by heat and/or pressure, from a solid to a viscous liquid by melting, at which point it can be readily applied to a coated abrasive article backing. Both hot melt and melt processable resin compositions can be in the form of a solid film that is transfer coated to the backing. Desirably, the hot melt compositions of the invention can be formulated as solvent free systems (that is, they have less than 1% solvent in the solid state).
However if so desired, it may be feasible to incorporate solvent or other volatiles into the binder precursor. As used herein, a xe2x80x9cpressure sensitive adhesivexe2x80x9d refers to a hot melt composition that, at the time abrasive particles are applied thereto, displays pressure sensitive adhesive properties. xe2x80x9cPressure sensitive adhesive propertiesxe2x80x9d means that the composition is tacky immediately after application to a backing and while still warm and, in some cases, even after it has cooled to room temperature. xe2x80x9cEVAxe2x80x9d means ethylene-vinyl acetate copolymer and xe2x80x9cepoxyxe2x80x9d means epoxide containing material or epoxy resin.
In a further embodiment of the present invention, a size coat, that is, a second binder, can be applied upon the make coat and abrasive particles to reinforce the attachment of the abrasive particles to the backing. A supersize coat, that is, a third binder, over the size coat, also may be used.
The make coat precursor or binder precursor may be in a solid form prior to coating and can be coated as a liquid solution or a molten mixture.
The invention additionally relates to use of the preferably energy curable, hot melt pressure sensitive first binder as a backing treatment coating for porous cloth materials to function, for example, as a saturant coat, a presize coat, a backsize coat, or as a subsize coat, to protect the cloth fibers and/or to seal the porous cloth material. If liquefied, the binder precursor can be coated as a size coat. Preferably, any backing treatment applied to the coatable side of the backing, for example, presize, is cured or crosslinked before a precursor and abrasive particles are applied to the treated surface of the backing. The cured coating or treatment on the backing is preferably substantially free of abrasive particles.
The binder precursors of the present invention also generally have a longer open time, better film-forming properties (which allows for formulating at lower levels), and lower cost than polyester/epoxy melt processable make resins. The binder precursors of the invention also have significant tack in the uncured state, controlled flow during curing, and desirable physical properties in the cured state, including adhesive and cohesive strength.